1 #include <map>
 2 #include <cmath>
 3 #include <vector>
 4 #include <cstdio>
 5 #include <cstdlib>
 6 #include <cstring>
 7 #include <iostream>
 8 #include <algorithm>
 9 # define maxn 300
10 using namespace std;
11 typedef long long LL;
12 LL m,F;
 
13 int n;
14 struct Food{
15     LL tim,p;
16 }g[maxn];
17 bool cmp(const Food a,const Food b){
18     if(a.tim==b.tim) return a.p>b.p;
19     return a.tim<b.tim;
20 }
21 Food q[maxn];
22 int head,tail;
23 void init(){
24     scanf("%lld%lld%d",&m,&F,&n);
25     for(int i=1;i<=n;i++) scanf("
 
%lld%lld",&g[i].p,&g[i].tim);
26     sort(g+1,g+n+1,cmp);
27     head=tail=1;
28     for(int i=1;i<=n;i++){
29         while(head<tail && g[i].p<q[tail-1].p) tail--;
30         q[tail++]=g[i];
31     }
32     for(int i=1;i<tail;i++) g[i]=q[i];
33     n=tail-1;
34 }
35 LL check(LL x){
 
36     LL rm=m-F*x, mt=0, ret=0;
37     LL tmp;
38     for(int i=1;i<=n;i++){
39         if(mt<=g[i].tim){
40             tmp=g[i].tim-mt+1;
41             tmp=min(tmp,rm/(g[i].p*x));
42             ret+=tmp*x;
43             rm-=g[i].p*tmp*x;
44             mt+=tmp;
45         }
46         if(mt<=g[i].tim){
47             tmp=min(x,rm/g[i].p);
48             ret+=tmp;
49             rm-=tmp*g[i].p;
50             mt++;
51         }
52     }
53     return ret;
54 }
55 void work(){
56     LL l=1,r=m/(g[1].p+F),mid1,mid2,ans=0,v1,v2;
57     while(l<=r){
58         mid1=l+(r-l)/3,mid2=r-(r-l)/3;
59         v1=check(mid1); v2=check(mid2);
60         if(v1<v2) ans=max(ans,v2),l=mid1+1;
61         else if(v1>v2) ans=max(ans,v1),r=mid2-1;
62         else ans=max(ans,v1),l=mid1+1,r=mid2-1;
63     }
64     cout<<ans<<endl;
65 }
66 int main(){
67     // freopen("a.in","r",stdin);
68     init();
69     work();
70 }

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